Radionuclide cardiac studies are useful in the management of patients with congenital heart disorders. Serial studies obtained before and after therapeutic interventions can objectively document the efficacy of medical or surgical therapy. Moreover, the simplicity of these studies also makes them well suited for evaluation of cardiac function during exercise. This study will assess the importance of rest and exercise measurement of left ventricular function in children with congenital valvular stenosis and insufficiency and in patients following repair of congenital heart disorders especially tetralogy of Fallot and transposition of the great arteries. The prognostic implications of measurements of cardiac function at rest and exercise will be evaluated in children with hypertension, cardiomyopathies and chronic tachycardias and anomalous coronary arteries. Resting studies will be used in the neonatal period to evaluate the cyanotic infant and to provide serial measurements of intracardiac shunting. The effects of hypoxia associated with birth trauma upon cardiovascular function will be assessed. A second major emphasis of this investigation will be improvement of radionuclide angiocardiogram techniques which are applicable to children. A multi-wire proportional gamma camera will be used because of the high counting rate and portability of this device. An improvement in methodology of equal importance would be the reduction of radiation dose by use of a radionuclide with a shorter half-life. Improvement in methodology and a clear definition of indicated uses of radionuclide angiocardiography should improve the management of patients with congenital heart disease.